Interpretive Summary: The naturally occurring endophytic funguses, Neotyphodium ceonophialum, provide the benefit to tall fescues of persistence; however, most natural occurring endophytes in tall fescues produce chemicals toxic to livestock. Novel endophytes have been developed and introduced to tall fescues that do not produce toxic chemicals; the new combinations of endophytes and tall fescues must be evaluated before their release. This research was conducted to compare two novel endophyte infected tall fescues to a native endophyte infected Kentucky-31 tall fescue and an endophyte-free tall fescue in the Coastal Plain region of Arkansas. Eleven, 2-acre pastures were planted to Kentucky-31, endophyte free (Barcel, Barenbrug USA, Tangent, OR), or the novel endophyte tall fescue varieties BarOptima infected with the E-34 endophyte (BarOptima PLUS E-34, Barenbrug USA) and Jesup infected with the AR542 endophyte (MaxQ, Pennington Seed Inc., Madison, GA). Pastures were grazed by growing beef calves for 2-yr beginning in January. Grazing was managed using the put-and-take method with tester cattle and additional calves were added as needed to maintain equal grazing pressure. After two grazing seasons, pastures contained an average of 83, 78, 70, and 9% stand coverage for Kentucky-31, Jesup AR542, BarOptima PLUS E-34, and Barcel, respectively. Across the grazing seasons, serum prolactin, ADG, total BW gain, and BW gain/ha were greater for endophyte free and novel endophyte tall fescues than for Kentucky-31. These results indicate that these two novel endophyte tall fescues are as persistent as Kentucy-31 in the Coastal Plain of Arkansas and animal performance is greater. Decreases in serum prolactin concentrations of calves grazing Kentucky-31 compared to endophyte free and novel endophyte tall fescue indicate that fescue toxicosis limited performance of calves grazing Kentucky-31 pastures, but was not a factor in novel endophyte pastures.

Technical Abstract:
New varieties of novel endophyte (NE) tall fescue must be evaluated before their release. This research was conducted to compare 2 NE infected tall fescue varieties to native endophyte infected Kentucky-31 (KY-31) and endophyte-free (EF) tall fescue in the Coastal Plains region of southwestern Arkansas. Eleven, 0.81-ha pastures were planted to KY-31 (n = 3), EF (cv. Barcel, Barenbrug USA, Tangent, OR, n = 3), or the NE tall fescue varieties BarOptima infected with the E-34 endophyte (BarOptima PLUS E-34, Barenbrug USA, n = 3) and Jesup infected with the AR542 endophyte (MaxQ, Pennington Seed Inc., Madison, GA, n = 2). Pastures were grazed by growing beef calves (n = 33, initial BW = 244 ± 9.5) for 2-yr beginning in January of each year. Grazing was managed using the put-and-take method, where 3 calves were used as tester animals to measure performance, and additional calves were added as needed to maintain equal grazing pressure among pastures. After 2 grazing seasons, pastures contained an average of 83, 78, 70, and 9% stand coverage for KY-31, Jesup AR542, BarOptima PLUS E-34, and Barcel, respectively. Across the 2 grazing seasons, serum prolactin, ADG, total BW gain, and BW gain/ha were greater (P < 0.07) for EF and NE tall fescues than for KY-31. In March and April of year 2, the percentage of observation points where calves were grazing was less (P < 0.05) in KY-31 than EF or NE pastures. The results of this study indicate that these 2 NE tall fescues are as persistent as KY-31 in the Coastal Plains of Arkansas and animal performance of calves grazing NE tall is greater than calves grazing KY-31. Decreases in grazing activity and serum prolactin concentrations of calves grazing KY-31 compared to EF and NE tall fescue indicate that fescue toxicosis limited performance of calves grazing KY-31 pastures, but was not a factor affecting NE pastures.